Overhead lines (overhead lines) serve for the transmission of electricity through wires laid in the open air and fixed on special supports or brackets of engineering structures with insulators and fittings. The main structural elements of the overhead line are wires, protective cables, supports, insulators and linear reinforcement. In urban conditions, VLs were most prevalent in the suburbs, as well as in up-building areas up to five floors. Elements of overhead lines must have sufficient mechanical strength, therefore, in their design, besides electrical, mechanical calculations are also made to determine not only the material and cross-section of wires, but also the type of insulators and supports, the distance between wires and supports,
Depending on the purpose and location of the installation, the following types of supports are distinguished:
intermediate, designed to maintain the wires on straight sections of the lines. The distance between the supports (spans) is 35-45 m for a voltage of up to 1000 V and about 60 m for a voltage of 6-10 kV. Fastening of wires here is made with the help of pin insulators (not tightly);
anchor, having a more rigid and sturdy construction in order to perceive longitudinal forces from the tension difference on the wires and to maintain (in case of breakage) all the remaining wires in the anchorage. These supports are also installed on the straight sections of the route (with a span of about 250 m for a voltage of 6-10 kV) and at intersections with various structures. Fastening of wires on anchor supports is made tightly to hanging or pin-type insulators;
end, installed at the beginning and end of the line. They are a kind of anchor supports and must withstand the constantly acting unilateral pulling of the wires;
angled, installed in places where the direction of the route changes. These supports are strengthened by struts or metal braces;
special or transitional, installed in the intersections of high-voltage lines with structures or obstacles (rivers, railways, etc.). They differ from other supports of this line in height or design.
For the manufacture of supports used wood, metal or reinforced concrete.
Wooden supports depending on the design can be:
single;
A-shaped, consisting of two racks, converging at the top and diverging at the base;
three-legged, consisting of three converging to the top and diverging at the base of the pillars;
U-shaped, consisting of two racks, connected at the top by a horizontal traverse;
AP-shaped, consisting of two A-shaped supports, connected by a horizontal traverse;
compound, consisting of a rack and attachment (stepchild), attached to it with a band of steel wire.
To increase the service life wooden supports impregnated with antiseptics, significantly slowing down the process of decay of wood. In operation, antiseptic treatment is carried out by applying an antiseptic bandage in places susceptible to decay, with antiseptic paste pasting all cracks, junctions and cuttings.
Metal supports are made of pipes or profile steel, reinforced concrete - in the form of hollow round or rectangular racks with decreasing cross-section to the top of the support.
Insulators and hooks are used for fixing the wires to the supports, and insulators and pins for fastening to the traverse. Insulators can be porcelain or glass whip or pendant (in places of anchorage) execution (Fig. 1, a-c). They are firmly hooked on hooks or pins with the help of special polyethylene caps or pakli, impregnated with wax or linseed oil.
Picture 1. a - pin 6-10 kV; b - pin 35 kV; in - suspended; g, d - rod polymeric
Insulators overhead lines are made of porcelain or tempered glass - materials that have high mechanical and electrical strength and resistance to weathering. An important advantage of glass insulators is that when damaged, tempered glass is sent. This makes it easier to find damaged insulators on the line.
By design, the insulators are divided into pins and pendants.
Pin insulators are used on lines up to 1 kV, 6-10 kV and, rarely, 35 kV (Fig. 1, a, b). They are attached to the supports using hooks or pins.
Suspended insulators (Figure 1, c) are used on overhead lines with a voltage of 35 kV and above. They consist of a porcelain or glass insulating part 1, malleable cast iron 2 caps, a metal rod 3 and a cement binder 4. Suspended insulators are assembled into garlands that are supported (on intermediate supports) and tensioned (on anchor supports). The number of insulators in a garland is determined by the line voltage; 35 kV - 3-4 insulators, 110 kV - 6-8.
Polymer insulators are also used (Fig. 1, d). They are a core element made of fiberglass, on which there is a protective coating with ribs made of fluoroplastic or silicone rubber:
The wires of the overhead line require sufficient mechanical strength. They can be single- or multiwire. Single-wire wires made of steel are used exclusively for lines up to 1000 V; stranded wires made of steel, bimetal, aluminum and its alloys have received a predominant distribution due to increased mechanical strength and flexibility. Most often, overhead lines with a voltage of up to 6-10 kV use aluminum multiwire wires of grade A and steel galvanized wires of the PS mark.
Steel-aluminum wires (Fig. 2, c) are applied to overhead lines with voltages above 1 kV. They are available with different ratios of aluminum and steel sections. The lower this ratio, the higher the mechanical strength is the wire and therefore is used in areas with more severe climatic conditions (with a greater thickness of the ice wall). In the steel and aluminum wire brand, the sections of aluminum and steel parts, for example, AC 95/16, are indicated.
Figure 2. a is a general view of the stranded wire; b - section of aluminum wire; c - cross section of steel-aluminum wire
Wires made of aluminum alloys (AH - not heat treated, AH - heat treated) have a greater mechanical strength compared to aluminum, and almost the same electrical conductivity. They are used on overhead lines with voltages above 1 kV in areas with an ice wall thickness of up to 20 mm.
The wires are arranged in various ways. On single-line lines, as a rule, they have a triangle.
Currently, the so-called self-supporting insulated wires (SIP) with voltage up to 10 kV. In a 380 V line, the wires consist of a bare, bare wire, three isolated line wires, one insulated outdoor wire. Linear insulated wires are wound around the carrying zero wire. The carrier wire is steel-aluminum, and linear - aluminum. The latter are coated with light-resistant thermally stabilized (cross-linked) polyethylene (APV type wire). To the advantages of VL with insulated wires before the lines with bare wires can be attributed the absence of insulators on the supports, the maximum use of the height of the support for suspension of wires; there is no need to prune the trees in the area of the line.
For branches from lines up to 1000 V, insulated wires of the APR or AWT brand are used for building entries. They have a bearing steel cable and insulation, resistant to weathering.
Fastening of wires to supports is made in various ways, depending on the location of their location on the insulator. On the intermediate supports, the wires are fixed to the pin insulators with clamps or a binding wire of the same material as the wire, the latter at the attachment point not having bends. The wires located on the head of the insulator are attached head viscous, on the neck of the insulator - lateral viscous.
On the anchor, corner and end supports, wires with a voltage of up to 1000 V are attached by twisting the wires with a so-called "plug", wires with a voltage of 6-10 kV - a loop. On anchor and angular supports, in the places of passage through railways, thoroughfares, tram ways and at the intersections with various power lines and communication lines double suspension of wires is used.
The connection of the wires is made by spot clamps, crimped with an oval connector, an oval connector twisted by a special device. In some cases, welding with the use of termite cartridges and a special apparatus is used. For single-wire steel wires, lap welding can be used using small transformers. In spans between supports, it is not allowed to have more than two wire connections, and in the spans of intersections of overhead lines with different structures, the connection of wires is not allowed. On the supports, the connection must be made so that it does not experience mechanical forces.
Linear reinforcement is used for fixing wires to insulators and insulators to supports and is divided into the following main types: clamps, coupling fittings, connectors, etc.
Clamps serve for fixing wires and cables and attaching them to garlands of insulators and are divided into supporting, suspended on intermediate supports, and tension, used on anchor-type supports (Fig. 3, a, b, c).
Figure 3. a - supporting clamp; b - bolt tension clamp; c - pressed tension clamp; г - supporting garland of insulators; d - distance strut; e - oval connector; ж - compression connector
Coupling armature is intended for suspension of garlands on supports and connection of multi-chain garlands to each other and includes staples, earrings, ears, rocker arms. The bracket serves to attach the garland to the traverse of the support. The supporting garland (Fig.3, d) is attached to the crossbar of the intermediate support by means of an earring 1 which is inserted into the cap of the upper suspension insulator 2 by the other side. The eyelet 3 is used to attach the garland of the supporting clip 4 to the lower insulator.
Connectors are used to connect individual wire segments. They are oval and pressed. In oval connectors, the wires are either crimped or twisted (Figure 3, e). Pressed connectors (Figure 3, g) are used to connect wires of large cross sections. In steel and aluminum wires, the steel and aluminum parts are pressed separately.
Cables along with spark gaps, arresters and grounding devices serve to protect the lines from lightning overvoltages. They are suspended over phase conductors at 35 kV overhead lines and above, depending on the area for thunderstorm activity and support material, which is regulated by the "Rules for the installation of electrical installations." Lightning ropes are usually made of steel, but when used as high-frequency communication channels - made of steel and aluminum. On 35-110 kV lines, fixing the cable to metal and reinforced concrete intermediate supports without insulation of the cable.
To protect against lightning overvoltages of sections of overhead lines with a lowered level of insulation compared to the rest of the line, pipe arresters are used.
All metal and reinforced concrete supports on which the lightning protection cables are suspended or other means of lightning protection (spark gaps, spark gaps) of 6-35 kV lines are grounded on the overhead line. On lines up to 1 kV with deadly grounded neutral, the hooks and pins of the phase wires installed on the reinforced concrete pillars, as well as the reinforcement of these supports must be connected to the zero wire.
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Air communication lines, as a rule, are built along the iron, road, and sometimes dirt roads. In settlements, they pass along the streets, and in cities - often pass through the roofs of buildings. Air lines built along roads and streets are different from air lines running along the roofs of buildings, the type of supports. Lines in which pillars serve as pillars (wooden, reinforced concrete) are called pillars. Lines running along the roofs of buildings have supports in the form of metal racks and are called rack-mounts.
The air communication line consists of wires, supports, insulators, traverses, pins, hooks, wires for crosses, fasteners and some other elements. In Fig. 2.1 shows the main elements of the air line and the main distances between the pins and hooks. On the lines of radio transmission networks, subscriber and feeder transformers are also located on the supports. On the terminal and cable (in the places of the joint of overhead lines with cable) supports can also accommodate cable entry boxes, cabinets, parts of air inlet equipment and other elements.
Air communication lines are the cheapest type of linear structures, but they do not provide the necessary reliability and stability of electrical characteristics, which becomes especially important on lines with a large number of channels. In addition, over the circuits of overhead lines the possibility of creating a large number of channels is limited due to a relatively small frequency range (up to 150 kHz), which can be effectively used. When organizing a large number of channels, the cost of the channel kilometer of an overhead line becomes higher than when communication is organized over cable lines.
Air communication and radio transmission networks are a complex set of devices.
Air communication lines are steel, copper or bimetallic wires, which, with the help of insulators, are attached to the supports. Reliability of overhead lines is also low.
The air communication lines occupy a significant place in the general scheme of the linear communications structures of the Soviet Union. Their cost is determined by hundreds of millions of rubles.
The air communication lines are divided into three classes according to their purpose.
The air communication line has the following parameters: r0 2 84 Ohm / km; L0 1 94 mH / km; d0 0 70 μS / km; C0 6 25 nF / km.
Air communication lines consist of metal wires suspended from special supports and isolated from each other and relative to the ground by means of insulators.
The air communication line has the following parameters: r0 2 84 Ohm / km; L0 1 94 mH / km; d0 0 70 μS / km; C0 6 25 nF / km. This condition coincides with the condition for the absence of distortions, since in this case Zj] / L0 / C0, ce] / r0g0, with l / L0Co are independent of frequency.
PLAN
AIR COMMUNICATION LINES
Objectives of the lesson:
Educational - to ensure the assimilation and consolidation of knowledge on the topic studied in the previous lesson, to control the degree of mastering the basic knowledge on the topic of the previous lesson.
Developing - to develop cognitive processes (attention, imagination, memory, perception).
Educational - to develop a positive attitude towards knowledge.
Lesson Type: Combined
Security of the lesson: insulators, hooks.
Intersubject communications: Technical means of railways, Stations and nodes.
Time: 2 hours
Purpose and classification of communication lines
Requirements for communication lines
Classification of overhead communication lines
Elements of VLAN
Organizing time.
Frontal survey on the topic of the previous lesson.
Statement of new material:
Fixing the material.
Assignment to the house: textbook LA. Kondratieva, ON Romashkova "Regulatory systems
traffic on the railway. transport "with. 297-298
AIR COMMUNICATION LINES
Purpose and classification of communication lines
LANs are designed to connect telephone or telegraph equipment installed in various locations.
Drugs by appointment are divided into 3 classes:
I class (backbone) - connect the Ministry with the management of roads and management between each other
II class (road and intra-division lines) - link management with departments, separation between each other and with large precinct stations
III class (local) - in-station, on the territory of large stations and nodes.
All drugs are divided into 2 types:
1). aerial lines of the VLAN
2). cable communication lines
Requirements for communication lines
the wires of the communication line must be isolated from each other (in the VLAN - air);
the lines of the communication line must be isolated from the ground;
the wires of the communication line must be protected from mutual interfering influences (protection-crossing, that is, the wires of the same circuit are swapped through a certain number of spans);
wire communication lines must be protected from dangerous influences contact network electrified railways;
wires of the communication line must be protected from lightning discharges (lightning conductor - steel wire 5 mm in diameter above the support by 15 cm, deepened into the ground by 0,7 m)
Classification of overhead communication lines
VLS have a great mechanical strength, have long service life, allow communication over long distances (up to 250 km). The advantage of overhead communication lines is also the ease of detection and repair of damages.
Durability depending on the weather conditions, VLANs are divided into 4 types:
1. O (light) - for southern regions with low ice intensity on wires (thickness of ice less than 5 mm)
2.N (normal) - for areas with an average glaze intensity (ice up to 10 mm)
3. U (strengthened) - for areas with a high intensity of ice (up to 15 mm)
4. OS (especially strengthened) - for areas with a particularly strong glaze ice (20 mm or more)
On the profile of the used supports VLANs are divided into:
with hook profile (low-conductor lines, up to 12 wires)
with a traverse profile (multi-wire lines up to 40 wires)
with a mixed profile
4. ELEMENTS OF VLAN
1. Supports
wooden
Wooden supports are made of trees with sufficient mechanical strength (oak, pine, spruce, larch, fir).
Impregnation with antiseptics (zinc chloride, creosote oil) - to extend the life of wooden supports.
reinforced concrete
All supports are subdivided:
simple
complex (anchor, semi-anchor) Used for the stability of lines with a traverse profile, for the device of transitions through railroad cars, with elongated spans, when changing from overhead communication lines to cable lines.
2. Fittings
The fittings include:
- hooks
(on the horizontal part they have a thread for screwing into the supports);
- insulators
(porcelain, glass, plastic);
- traverses
(typical eight-pin)
3. Wires.
Wire is used as a wire - steel, copper, bimetallic.
Steel - high mechanical strength, low cost; low electrical conductivity, is susceptible to corrosion. For protection against corrosion, zinc or add 0.2 - 0.4% copper (with copper additive)
Copper - high electrical conductivity, not subject to corrosion; high cost, less durable;
Bimetallic - is a steel core with a diameter of 3.2 mm with an outer copper layer of 0.4 mm.